<p>Hi David,
<p>
In my opinion use 3.x if:
<ul>
<li>Site has many users and requires good performance. Since 4.x permissions may not yet scale well.
<li>You need a module has is not yet present in 4.x and is very hard to port or no 4.x modules may substitute for it.
<li>You are sure that the site will not use 4.x features now and the future.
<li>There is little chance of upgrading to 4.x
</ul>
Use 4.x if:
<ul>
<li>site needs or greatly benefits from the new features of 4.x like complex permissions, CMS/CR, templating, etc.
<li>site may need or outgrow what 3.x offers.
</ul>
<p>
You may also want to talk to your client regarding this. Well you have to put into lay man terms the problems and scenarios. For me I picked 4.x on site since it was relatively light load and deadlines can be moved. I picked 3.x on another site since I need to make it in 1 week and did not require any 4.x specific features. Look at the short term plus and minus if its going to be a short term project otherwise look at the long term plus and minus. OpenACS 4.x is not in a bad shape, infact its in a good shape considering its on alpha release. Also bear in mind that OpenACS 4.x was based on ACS 4.2. Good luck in your work.
